linux-kernel - Re: [PATCH v10 03/11] x86/cpufeatures: Add TDX Guest CPU feature

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Date:   Wed, 13 Oct 2021 12:42:51 -0700
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Juergen Gross <jgross@...e.com>, Deep Shah <sdeep@...are.com>,
        VMware Inc <pv-drivers@...are.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, Peter H Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v10 03/11] x86/cpufeatures: Add TDX Guest CPU feature

On Wed, Oct 13, 2021 at 10:18:18AM +0200, Borislav Petkov wrote:
> On Fri, Oct 08, 2021 at 10:37:39PM -0700, Kuppuswamy Sathyanarayanan wrote:
> > @@ -500,6 +501,14 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
> >  
> >  	copy_bootdata(__va(real_mode_data));
> >  
> > +	/*
> > +	 * A future dependency on cmdline parameters is expected (for
> > +	 * adding debug options). So the order of calling it should be
> > +	 * after copy_bootdata() (in which command line parameter is
> > +	 * initialized).
> > +	 */
> 
> Plain and simple:
> 
>         /*
>          * Keep this after copy_bootdata() so that TDX cmdline options can take
>          * effect.
>          */

But there are no actual TDX cmdline options in this patch set, which is
why I originally asked for clarification in the comment.

> > +	tdx_early_init();
> > +
> >  	/*
> >  	 * Load microcode early on BSP.
> >  	 */
> > diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
> > new file mode 100644
> > index 000000000000..88bf12788684
> > --- /dev/null
> > +++ b/arch/x86/kernel/tdx.c
> > @@ -0,0 +1,38 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/* Copyright (C) 2020 Intel Corporation */
> > +
> > +#undef pr_fmt
> > +#define pr_fmt(fmt)     "tdx: " fmt
> > +
> > +#include <asm/tdx.h>
> > +
> > +bool is_tdx_guest(void)
> > +{
> > +	static int tdx_guest = -1;
> 
> Put that one at the top of the file because such static variables do not
> belong among the automatic function vars.

I disagree, this prevents confusion and misuse by making it clear that
the scope of the static variable is limited to this function.

-- 
Josh